1. Field of the Invention
The present invention relates to signal processing in a Japanese audio broadcast signal.
2. Related Art
The Japanese Broadcast Television Systems Committee (“JBTSC”) standard audio broadcast signal has three modes of transmission. These modes are mono, stereo, and dual mono. To serve both stereo and non-stereo television sets, the JBTSC standard requires the left (“L”) and right (“R”) channels of a stereo signal to be summed and transmitted as one signal in the space normally occupied by the mono audio signal. The summed L+R output, called the main channel signal, provides the mono signal of the original audio program content. This summed signal may be received by non-stereo television sets.
In stereo mode, the JBTSC system sends an L−R signal (herein referred to as “sub”), which is the difference between left and right channels. While this signal alone cannot be used by the television set, it is essential to reconstructing the stereo signals (L and R). In dual mono mode, the second mono audio program is transmitted in the sub channel.
A third channel, called the control channel, is inserted into the transmission to indicate whether the broadcast is in mono, stereo, or dual mono mode. This channel is AM modulated and requires a detector to figure out the actual broadcast mode.